Image input systems such as cameras or camcoders, zoom lenses that can vary their focal length are used widely to obtain zoom images, conventionally.
However, as the zoom lens is highly precision instrument, it is expensive and also large in size. Especially, for the digital zoom cameras that have been required to be small size and low price, conventional zoom lenses were obstacles for these requirements. Furthermore, as image input devices or image sensors such as CCDs have been becoming small in size recently, smaller and shorter focal length zoom lenses have been required for cameras that use these devices.
But, it is very difficult to realize the wide angle zoom lens in short focal length, as it become very small and complicated.
On the other hand, in the case of three-dimensional(3D) zoom image input, accurately synchronized zoom action between two zoom lenses for the left and right images become necessary. As such a synchronized zoom action has to be achieved precisely all in mechanical at the conventional zoom lens, it becomes a very complicated and expensive apparatus. Consequently, the introduction of zoom lens to 3D image input has been very difficult.
Sometimes, in digital cameras, it is called as the electronic telephoto zooming to expand simply a part of the input image electronically. But it differs from a real zoom action, because the resolution of the zoom image is degraded along with its expansion.